398 Professor Sedgwick and Mr. Murchison on the 



This portion of the rock has occasionally the external appearance and fracture 

 of English cornbrash ; and exhibits stellated impressions of black oxide of iron 

 on its broken surfaces. 



These quarries are surmounted by white, green, and iron-stained calcareous 

 sands, finely laminated in wavy lines ; and above them are repetitions of blue, 

 yellowish, and green, arenaceous marl, similar to that described from a lower 

 part of this section. 



The total thickness of all the strata, from the base of the hill, cannot be 

 estimated at less than five or six hundred feet. From the evidence of the or- 

 ganic remains, as well as from the position and strike of the strata, there can be 

 no doubt that the group at Poppendorf is of the same or nearly the same age 

 as that of Radkersberg; and thus we find, that one of the last operations in 

 the formation of these great tertiary deposits, was the production of an oolite, 

 undistinguishable in many parts of its structure from the great oolite of 

 England*. 



By referring to the accompanying section (fig. 15.), it will be seen, that in 

 the adjoining hill, the shelly sands and marls have not been deposited in the 

 same manner as at Poppendorf; but have been broken in upon by eruptions 

 of volcanic matter. These striking phenomena are seen in the hill of Perish, 

 between Poppendorf and Gnaess, the base of which (at the point where we 

 examined it, in a little combe on its south-eastern side), consists of a coarse 

 volcanic tufa and breccia, made up of earthy matter, containing many frag- 

 ments of basaltic lava, scoria, decomposing ancient rocks, cjuartz pebbles, 

 crystals of vitreous felspar, olivine, and pyroxene, mixed up with broken ter- 

 tiary shells. 



A little above this tufaceous deposit, thick beds of the tertiary calcareous 

 sandstone alternate with a similar volcanic mass; and further in the ascending 

 series, some of the volcanic beds contain many well-preserved shells. Green, 

 micaceous, and calcareous sand of considerable thickness succeeds ; and it is 

 surmounted by a regularly bedded, greenish, dark-coloured volcanic breccia, 

 seven or eight feet thick, which is nearly horizontal, and so indurated as to be 

 much quarried for building. 



This volcanic rock contains crystals of decomposing glassy felspar ; olivine ; 

 much scoriaceous and basaltic lava, with olivine and pyroxene; many fragments 

 of shells ; and pebbles probably derived from the shingle banks of the tertiary 



* Considered as a suite, the shells at Poppendorf and Radkersberg are very nearly the same. 

 For a much more complete account of the fossils at all the localites above mentioned, we must 

 refer to the list at the end of this paper, and to Plate XXXIX. accompanying it. 



